1. Field of the Invention
The present invention relates to a method for joining edge portions of electromagnetic wave shielding members each consisting of a metal foil or a metal sheet and exhibiting an excellent electromagnetic wave shielding performance.
2. Description of the Prior Art
As a method for joining edge portions of metal sheets and metal foils exhibiting an excellent electromagnetic wave shielding performance for the purpose of insuring electromagnetic shielding in a shield room or the like, the following classes of methods are generally practiced.
i) Superposed seam folding method: PA1 A method of insuring a two-dimensional contact area of electromagnetic wave shielding members per se by superposing the above-mentioned shielding members on one another and carrying out seam folding. PA1 ii) Sticky layer associated metal foil tape sticking method: PA1 A method of sticking a metal foil tape b having an electrically conductive sticky layer a on its back surface onto edge portions of electromagnetic wave shielding members c made of metal foils, thereby sticking and joining the above-mentioned metal foil tape onto the same edge portions via the above-mentioned sticky layer (see FIG. 4). PA1 iii) General solder-joining method: PA1 A method of joining underlying edge portions of electromagnetic wave shielding members c by applying common thread-like solder or liquid solder d to edge portions of the electromagnetic wave shielding members c and thermally welding the same solder by means of a soldering iron (see FIG. 5). PA1 iv) Sealing material filling method: PA1 A method of joining underlying edge portions of metal foil shielding members c by applying electrically conductive sealing materials or puttying materials e onto and between the edge portions (see FIG. 6).
However, in the superposed seam folding method described in paragraph i) above, skill is required in carrying out the folding work. And, when a thin raw material such as a metal foil is used, the raw material is liable to be damaged due to its being folded back. Also the joint surface is remarkably uneven, and so the quality of the finished surface is poor.
In the sticky layer associated metal foil tape sticking method described in paragraph ii) above, since the sticky layer of the metal foil tape is formed by an electrically conductive filler to insure electrical conductivity with the underlying layers, the sticky layer itself does not exhibit such an excellent electromagnetic wave shielding performance. Consequently, electromagnetic waves can leak through the sticky layer, and therefore, it is difficult to insure a satisfactory shielding performance. In addition, due to variations in the adhesives, there is an anxiety concerning the reliability of adhesion over a long period of time.
In the general solder-joining method described in paragraph iii) above, a high degree of skill is required for the soldering work. Also, when the soldering is carried out on a vertical surface or on a ceiling, molten solder can drop therefrom. Hence, the work is technically difficult and at the same time there exists a safety problem. Furthermore, the joined surface is liable to be uneven, whereby the quality of the finished surface is poor.
Further in the sealing material filling method described in paragraph iv) above, like the above-mentioned sticky layer associated metal foil tape sticking method, although electrical conduction with the underlying layer is effected by means of the sealing material or puttying material mixed with electrically conductive filler, since the electromagnetic wave shielding performance of the sealing or puttying material is poor, the shielding performance exhibited by the overall joint is degraded. And, since a principal component of the sealing material or puttying material is a synthetic high-molecular compound, there exists a problem in its durability over a long period of time depending upon the environmental conditions under which it is used.